The MAC layer is the "Brain" of WiFi. The first version of 802.11 (the 802.11 legacy published in 1997), defined the MAC layer by incorporating a number of features crucial, such as sharing of speech among users, the terms of network connection, error control or security.

The MAC layer also defines the network addresses: all devices have an identifier of 48 bits (6 bytes) known as the "MAC address". The first three bytes identify the manufacturer of the network equipment. For example, in hexadecimal notation, 00-00-0c corresponds to Cisco constructor, 00-04-23 corresponds to Intel Corporation, etc. The following three bytes define an identifier one chosen by the manufacturer, for example 8B-B5-0B. An address will look like for example: 00-04-23-8B-B5-0B. Any network adapter (WLAN, Ethernet or other) therefore has in principle a MAC address, supposed to be unique. One can communicate with a device by sending packets on the network, denominated in its MAC address.

Other standardized protocols by the IEEE, such as Ethernet or Token Ring, have the same definition of the MAC address. This allows stations to different types of networks to communicate with each other: it suffices to connect different networks together with "bridges" (bridge). Many aspects of WLAN MAC layer are inspired directly from the MAC layer Ethernet, as we shall see, to the point that some refer WiFi as "Wireless Ethernet."